Miniature circuitry and inductive components and methods for manufacturing same

ABSTRACT

Miniature circuitry and inductor components in which multiple levels of printed circuitry are formed on each side of a support panel, typically a printed circuit board or rigid flex. Electrical connection between the plural levels of circuitry and multiple windings around magnetic members are provided by plural plated through hole conductors. Small through hole openings accommodate a plurality of the plated through hole conductors since each is insulated from the others by a very thin layer of vacuum deposited organic layer such as parylene having a high dielectric strength. Adhesion of this plated copper to the organic layer is provided by first applying an adhesive promotor to the surface of the organic layer followed by the vacuum deposition of the organic layer.

This application is continuation of U.S. application Ser. No.11/895,355, filed Aug. 24, 2007, which is a divisional of U.S.application Ser. No. 11/296,579, filed Dec. 7, 2005, now U.S. Pat. No.7,271,697, issued Sep. 18, 2007, which claims priority from U.S.Provisional Application No. 60/633,742 filed Dec. 7, 2004, the entiretyof each of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to improvements in miniature electricalcircuits and inductors and transformers and methods of manufacturingthese devices.

SUMMARY OF THE INVENTION

One aspect of the invention is a high yield process for manufacturingimproved miniature circuits, inductors and transformers having highfunctional reliability. In particular, the process fabricates two ormore independent and isolated conductors in the same via holes. Aspectsof this embodiment include closely spacing while maintaining a highvoltage barrier between the conductors and providing interconnectreliability.

For inductive embodiments, the two or more independent conductors areadvantageously fabricated on the wall of a hole either in or proximateto a ferrite member embedded in a cavity in a printed circuit board orflexible circuit. Embodiments include holes located in a ferrite plateand holes located around a ferrite toroid. These conductors function aswindings of an inductor or transformer.

In another embodiment, the two or more independent conductors are formedon the wall of vias in circuit board or flexible circuits tointerconnect circuits and circuit elements located on opposite sides ofthe printed circuit board or flexible circuit.

Extremely miniature devices are constructed by providing an extremelythin but very high dielectric film between plural plated through holeconductors in each via. In addition, further miniaturization is providedby utilizing printed circuits over the entire surface of the supportpanel and locating surface mounted components over the magnetic membersembedded within the support panel.

The miniaturization achieved by the circuits and processes enable, forexample, very small and lightweight power supplies for laptop computers,digital cameras, portable audio and T.V. devices, and cell phones.

The improved inductor and circuit configurations enable efficient andrepeatable manufacture of miniature circuits and miniature inductors andtransformers having high voltage, high current capabilities, as well ashigh tolerance to physical stress.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a support panel with aplurality of toroidal cavity openings routed therein;

FIG. 2A is a perspective view illustrating embedded ferrite toroids ineach of the routed cavity openings in the support plate;

FIG. 2B is a cross-sectional view along lines 2B-2B of FIG. 2A;

FIG. 3 is a cross-sectional view of the support panel having copperlayers on opposite sides;

FIG. 4 illustrates a cavity and the removal of the top copper layer fromthe support panel;

FIG. 5 is a cross-sectional view illustrating the lay-up prepreg ringsand prepreg copper foil lamination;

FIG. 6 is a perspective view of the toroid ferrite;

FIG. 7 is a cross-sectional view showing the assembly prior to thelamination of the copper foil;

FIG. 8 is a cross-sectional view showing the assembly after laminationof the copper foil;

FIG. 9 is a top elevational view showing the through via holes formedaround the outer and inner walls of the ferrite core;

FIG. 10 is a cross-sectional view of the via holes;

FIG. 11 is a cross-sectional view illustrating copper plating of theassembly;

FIG. 12A is a top elevational view showing the first layer of printedcircuit conductors;

FIG. 12B is a bottom elevation view showing the second layer printedcircuit conductors;

FIG. 13 is a cross-sectional view showing application of the firstinsulating layer over the first and second layers of printed circuit andover the first plated through hole;

FIG. 14 is a cross-sectional view showing the application of the secondinsulating layer;

FIG. 15 is a cross-sectional view showing the application of the thirdinsulation layer and adhesion promotor;

FIG. 16 is a cross-sectional view illustrating the lay-up of predrilledbond ply and copper foils;

FIG. 17 is a cross-sectional view showing the assembly after laminationof the copper foils;

FIG. 18 is a cross-sectional view showing transformer via holes etchedfrom the copper foils;

FIG. 19 is a cross-sectional view showing the copper plating over theassembly;

FIG. 20 is a cross-sectional view illustrating the lay-up prepreg andcopper foil before lamination;

FIG. 21 is a cross-sectional view illustrating the laminated assembly;

FIG. 22 is a cross-sectional view illustrating the application of acover layer or solder mask to the assembly;

FIG. 23 is a perspective view of a power supply in which the inductiveelements are embedded in the printed circuit panel;

FIG. 24 is a perspective view of another embodiment having a supportpanel having a plurality of rectangular openings;

FIG. 25 is a perspective view illustrating a support panel havingrectangular ferrite plates in each of the openings;

FIG. 26 is a cross-sectional view of an embodiment utilizing rectangularferrite plates;

FIG. 27 is an elevation view of a subassembly illustrating thetransparency of the parylene insulating layer;

FIG. 28 is a photomicrographic view of an exemplary cross-sectionshowing two parylene insulated conductive vias in a single via hole asformed by this invention;

FIG. 29 is a photomicrographic view of an exemplary cross-sectionshowing three parylene insulated conductive vias in a single via hole asformed by this invention; and

FIG. 30 is a photomicrographic view of an exemplary cross-sectionshowing four insulated conductor vias in a single via hole as formed bythis invention.

FIG. 31A is an elevational view of the first or top printed circuitlevel of another embodiment having two toroids embedded into the supportpanel;

FIG. 31B is an elevational view of the second or bottom printed circuitlevel of the embodiment of FIG. 31A;

FIG. 32A is an elevational view of the third printed circuit level, ofthe embodiment of FIG. 31A, formed in a plane proximate to and over theplane of the first printed circuit layer;

FIG. 32B is the elevational view of fourth printed circuit level formedin a plane proximate to and over the plane of the second printed circuitlevel of FIG. 31B;

FIG. 33A is an elevational view of the fifth printed circuit level ofthe embodiment of FIG. 31A, formed in a plane proximate to and over theplane of the third printed circuit level of FIG. 32A;

FIG. 33B is an elevational view of the sixth printed circuit level ofthe embodiment of FIG. 31A proximate to and over the plane of the fourthprinted circuit level of FIG. 32B;

FIGS. 34A and 34B are perspective views of the top and bottom of a powersupply constructed utilizing the printed circuit level shown in FIGS.31A, 31B, 32A, 32B, and 33A, 33 b;

FIG. 35 is a cross-sectional view illustrating the use of the platedthrough holes for both forming winding turns for conductors andtransformers and for providing electrical connections between otherprinted circuitry layers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The process for manufacturing one embodiment of inductive componentdevices is illustrated in FIGS. 1-22. As shown in FIG. 1, a plurality oftoroidal openings or cavities 50 are formed, typically by routing, in asupport panel 52. Panel 52 is advantageously an FR-4 epoxy laminatesheet 54 with copper layers 56, 58 on opposite sides, as shown in FIG.3, although it will be apparent that sheets made from other materialsincluding other types of sheets used for circuit board fabrication andrigid flex are applicable for use as support panel 52. Using standardtechniques of printed circuitry, the top copper layer 56 is theneliminated using the dry film to mask the bottom surface of the supportpanel. The exposed (unmasked) copper layer 56 is then etched off fromthe top surfaces of the panel. The remaining dry film mask is thenstripped from the bottom surface to provide a support panel having thecross-section shown in FIG. 4.

FIGS. 1 and 2A illustrate a support panel 52 on which four cavities areformed to simultaneously manufacture four inductor or four transformercomponents after which the support board is cut or mounted to produce aplurality of individual components such as illustrated in FIGS. 23, 34A,and 34B. It will be understood that the processes described below areusually used to simultaneously manufacture a larger number ofcomponents, typically in the range of 16 to 20 components. Also, eachcomponent may include a single cavity embedding a single magnetic toroidor may include two or more such cavities and toroids to produce two ormore embedded inductive devices for a particular electronic device. See,e.g., the power supply described below and shown in FIGS. 34A and 34B.

Following the cavity preparation, one or more prepreg toroidal rings 60are seated onto the bottom of each of the formed toroidal openings 50 asshown in FIG. 5.

Ferrite toroids 62 (shown in FIG. 6), are then respectively embeddedwithin the openings 50, as shown in FIGS. 2A and 2B. Each of theseferrite toroids 62 serve as a ferromagnetic slab for a fabricatedinductive component. By way of specific example, the toroid may have anoutside diameter of 1.25 inches and an opening of ⅜ inches. A copperfoil 70, is then laminated to the top surfaces of the ferrite toroid 62using an epoxy prepreg 72 or other suitable adhesive to affix the foilto the ferrite plate. Depending upon the ultimate application of theinductive component, the copper foil will typically also cover all orpart of the support panel 52.

The lay-up of the prepreg rings 60, ferrite toroids 62 and lay-upprepreg 63 and copper foil 70 is illustrated in FIG. 5. The laid-upsubassembly is shown in FIG. 7A.

As illustrated in FIG. 7B, panel 52 and assembled ferrite toroids,prepreg and copper foil are then placed in a holding fixture of alaminating machine (not shown) that applies pressure and heat resultingin the top surfaces of the ferrite cores 62 being made substantiallyflush with the top surfaces of board 52 and prepreg material filling thevoids between the walls of openings 50 and ferrite cores as well aslaminating the copper foil 70 over the cores 62 and support panel 52 asshown in FIG. 8. The resultant flat surface over the embedded toroidferrite permits multiple additional circuit layers and mounting ofcircuit elements over the entire support panel 56. As described below,extremely small components such as switching power supplies and batterychargers for laptops, computers, digital cameras, cell phones, portableaudio and TV's and the like can be constructed.

In this lamination step and the lamination steps described below, thematerials used are selected to provide the desired physical propertiesfor the finished circuitry. These properties are commonly referred to aspeel strengths and bond strengths. The preferred materials forlaminating are: Medium or High Tg epoxy prepregs from LG, Isola,Polyclad or Arisawa.

Through holes (vias) 80 and 81 are then respectively drilled through thelaminated subassembly panel 85 around the outside and inside of ferritetoroids using conventional drilling equipment. These via holes aretypically 12 to 50 mils in diameter. As described below, these throughholes or vias 80 and 81 (shown in FIGS. 9 and 10) enable fabrication ofplated through hole conductors which function as electrical windings forthe inductor or transformer device.

After drilling, the laminated panel 85 is advantageously plasma etchedto clean the drilled holes. This step is advantageously followed by aglass etch to remove spurious glass particles from the holes 80, 81 orroughen the glass fibre for adhesion of the copper plating followed bychemically cleaning the vias 80, 81 and the top and bottom surfaces ofthe exposed copper sheets 58 and 70.

A conventional process is then used to chemically coat the insidesurface of all of the through holes 80, 81. In one embodiment, theSHADOW process is utilized. Other processes include an electroles copperdeposition and DMSE/HDI process. An article describing the processentitled “The Reliability of PTH Printed Wiring Boards Manufactured Witha Graphite-Based Direct Metallization Process” is included with thisapplication as Appendix A.

Following this application of the chemical coating, the subassembly 85is copper plated. The plated copper 90 is shown in FIG. 11 and coversboth the copper foil laminate 58, the copper foil laminate 70 and theinternal walls of the through holes (vias) 80, 81 (shown at 95) so as toelectrically connect the top and bottom copper foils 58, 70 via theplated through holes 95.

Printed circuits 100, 101 (shown in FIGS. 12A and 12B) are thenfabricated using the top and bottom layers of the copper laminate 58, 70and plated copper 90. These circuits 100, 101 are advantageously formedby vacuum laminating a dry photographically developable film over thesurfaces of the plated copper on the top and bottom of the subassembly.Using standard, well known techniques of printed circuitry, first layer100 and second layer 101 of circuitry are fabricated by using the dryfilm to mask the desired circuitry. The exposed, i.e., unmasked copperis then etched from both top and bottom surfaces of the componentassembly. The remaining dry film mask is then stripped from those topand bottom surfaces. The remaining copper forms a first layer ofcircuitry 100 on the top surface (shown in FIG. 12A), and a second layerof circuitry 101 (shown in FIG. 12B) on the bottom surface,interconnected by the copper plated via holes 95. As described below,these formed printed circuits respectively include circuits 100, 101which are respectively connected at each end to a plated through hole80, 81 to provide a continuous, electrical winding around the ferritecore encased in the support member. These windings and ferrite core forma miniature inductor transformer.

The top and bottom surfaces are then chemically cleaned. The componentassembly is then vacuum baked to remove any remaining moisture.

The component assembly is then prepared for an additional copper layerand an additional plated via insulated from but fabricated over thefirst copper layers. An insulating coating is used to separate themultiple layers of circuitry and plated vias. Epoxy, polymer, liquidpolyamide and other materials may be used. However, parylene coating hasbeen discovered to be particularly advantageous for forming theseinsulating layers. Parylene is an organic coating with an inert surface.In one embodiment, in preparation for the parylene coating, an adhesivepromotor such as a very thin Silane, Carboxyl or Silane and Carboxyllayer 110 (shown in FIG. 13) is deposited on the subassembly includingthe top and bottom surfaces and walls of the plated through holes usinga PECVD process (Plasma Enhanced Chemical Vapor Deposition) or othersuitable process. In another embodiment, this very thin layer 110 may beformed by dipping the subassembly in a Silane or other adhesive beforedeposition of the parylene.

The parylene is then vacuum deposited over the entire subassembly toleave, as illustrated in FIG. 14, a thin coating 115 over the first(top) layer of circuitry 100, a thin coating 116 over the second(bottom) layer of circuitry 101 and a thin coating 117 over (inside) thecopper plated through hole 95.

The parylene coating process is further described in the publicationentitled “Parylene Conformal Coatings Specifications and Properties,”published by Specialty Coating Systems, Indianapolis, Ind. and attachedas Appendix B to this application. This parylene coating is pinhole freeand has a high dielectric strength with very thin coatings providingvery high voltage breakdown values. By way of specific example, parylenecoatings formed of Parylene C with thicknesses of 0.0005 mil to 0.001mil provide a voltage breakdown guard band of about 5600 volts per milof thickness. Parylene C has a dielectric constant of about 2.28.

Nova HT Parylene described in Appendix C to this application provides aneven higher dielectric constant of about 3.15 and provides a voltagebreakdown of about 750 volts per micron of thickness. As a result, verythin coatings, e.g. 10 to 15 microns provides a breakdown voltagebarrier in the range of 7500 volts or higher.

A parylene coated subassembly is shown in FIG. 27. This and otherparylene coatings shown in other photographs were coated at the SCSCoating Center at Ontario, Calif., as described in Appendix D to thisapplication.

The thickness of the deposited parylene layers 115, 116 and 117 isdetermined by several factors including physical size of themanufactured inductor or transformer, physical size of the through holeopenings 80, 81, the number of insulated plated through hole conductorsto be formed in a through hole, and the power rating of the manufacturedproduct. For the miniature inductors and transformers described below,the thickness of the parylene layer will be in the range of about 0.5mil to 3 mils. (0.0005 to 0.003 inches), and the breakdown guard bandwill be in the range of about 5600 to 15,000 volts per mil of thicknessof the parylene layers.

The extremely thin parylene provides a high dielectric coating betweenthe copper plated through holes and enables plural such through holeconductors to be formed in a very small through hole opening. A furtheraspect of the these coatings that enables multiple conductors through asingle very small via is that the vacuum deposited parylene provides asubstantially uniform thickness coating that closely follows the contourof the underlying copper plate. As a result, the parylene does not, ofitself, cause an unpredictable build up of thickness in the platedthrough hole. The diameter of the through holes will typically bedetermined by the thickness of the support panel 56 and the number ofplated, through holes to be formed in each through hole. The panelthickness is typically in the range of about 62 mil to 15 mil. Typicallythe hole size will range from about 12 mil to 50 mil. For a panel 90 milthick, a hole size of about 22 mil diameter will typically be used toform two plated through holes within this through hole and a hole sizeof about 40 mil diameter will be selected to form four plated throughholes. For a thicker panel 0.125 mil thick, a hole size of about 28 milwould typically be used to form two plated through holes and a hole sizeof about 40 to 60 mil will typically be used to form four plated throughholes.

While having excellent dielectric insulative properties, the surface ofthe deposited parylene will not bond or adhere to plated copper. It hasbeen discovered, however, that a suitable adhesive promoter isaccomplished by adding a positively charged moiety to the backbone ofthe parylene compound. This is advantageously accomplished by using theplasma enhanced chemical vapor deposition (PECVD) process. In oneembodiment, the process is a Carboxl or Silane gas phase chemicalreactions at low pressures (10 to 500 mT), voltages typically in therange of about 200 to 700 volts, currents typically in the range ofabout 3 to 7 amp and power in the range of about 6V to 2000 watts. Theresulting surface (indicated at 120 in FIG. 15) populated with reactivesites, ready to receive an adhesive or coating. The mechanism isbelieved to be primarily due to hydrogen bonding and covalent bondingdue to this adhesive or coating reacting to the changed moiety.

Formation of third and fourth layers of circuitry begins with drillinghole openings 122, 123 in adhesive sheets 125, 126 before these sheetsare positioned onto the assembly. These openings 122, 123 are drilled toregister over the first and second layer circuitry openings 80, 81. Asshown in FIG. 16, the pre-drilled adhesive sheets 125 and 126 are thenrespectively positioned over the top and bottom surfaces of thesubassembly. A low temperature lamination process is then used topartially laminate the pre-drilled adhesive sheet 125, to the surface ofthe parylene coated top surface of this top circuitry layer 100 andadhesive sheet 126 to the surface of the parylene coated bottomcircuitry layer 101, as shown in FIG. 12B. Copper foil 130, is thenattached to the top side of the adhesive coated panel and copper foil131 is attached to the bottom side of the adhesive coated panel.

Copper foils 130, 131 are then laminated to the subassembly at hightemperature and pressure to form a four copper layer assembly shown inFIG. 17 with the third layer 130 and the fourth layer 131, respectively,insulated from the circuitry layers 100, 101 by the insulating layers110, 115, 116, 120.

Using the well known techniques of printed circuitry, via holes 135,136, 137, and 138 (shown in FIG. 18) are formed in the copper foils 130,131 by using the dry film to mask the copper. The unmasked copper isthen etched from both top and bottom surfaces of the component assemblyto form these vias 135-138. The remaining dry film mask is then strippedfrom those top and bottom surfaces.

The surfaces of copper foils 130, 131 are now chemically coated usingthe SHADOW process. Following the application of a chemical coatingusing the SHADOW process, the subassembly is again copper plated. Theplated copper 145 is shown in FIG. 19 and covers both the copper foillaminate 130, copper foil laminate 131 and the parylene coated walls ofthe plated through holes 95 so as to form second conductive throughholes 140 in the same through hole and thereby electrically connect thethird and fourth copper plated foils 130, 131.

Third and fourth printed circuits 150, 151 are then fabricated using thetop and bottom layers of plated copper foils 130, 131. These circuitsare advantageously formed by vacuum laminating a dry photographicallydevelopable film over the top and bottom surfaces of the plated copper.Using standard well known techniques of printed circuitry, these thirdand fourth layers of circuitry are fabricated by using the dry film tomask the desired circuitry. The exposed (unmasked) copper is then etchedfrom both top and bottom surfaces of the component assembly. Theremaining dry film mask is then stripped from those top and bottomsurfaces. The remaining copper forms the desired third layer ofcircuitry 150 on the top surface, the fourth layer of circuitry 151 onthe bottom surface, and the circuitry connections between layers 150,151 provided by the copper plated via holes 140.

The top and bottom surfaces are then chemically cleaned. The componentassembly is then vacuum baked to remove any remaining surface chemicals.

Additional fifth and sixth layers of circuitry 160, 161 are fabricatedover the third and fourth layers. In the embodiment shown in FIG. 20,these circuit layers are insulated from the adjacent third and fourthlayers by two layers of prepreg 165. By way of example, the Isola mediumTg epoxy prepreg has a voltage breakdown rating of 1100 to 1200 voltsper mil thickness. By way of specific example, a 4 mil thickness of thisprepreg was used to provide a voltage breakdown of over 4000 volts.These fifth and sixth circuit layers are formed following the cleaningand baking steps as follows:

-   -   1) Drill the fifth layer 160 and sixth layer 161 copper foils        with tooling holes    -   2) Drill tooling holes in two sheets of adhesive, or prepreg    -   3) Lay up two additional adhesive coated copper foils 160, 161,        or copper foil and prepreg on to the assembly shown in FIG. 19        containing four layers of circuits    -   4) Laminate all the material together at high temperature and        pressure using a vacuum lamination process so the result at this        stage of manufacture is an assembly shown in FIG. 21 having six        copper foil layers 58, 70, 130, 131, 160 and 161 with circuit        layers 58 and 70 interconnected via the plated holes 95 and        circuit layers 130 and 131 interconnected by plated holes 140        which are isolated from the plated holes 95 but using the same        via holes    -   5) As shown in FIG. 35, additional through holes 153 may now be        selectively drilled through the respective plated copper sheets        and support panel 56 to enable, for example, through hole        connectors for surface mounted circuit elements, e.g.,        semiconductors, capacitors, resistors located over the cavity 50        and embedded toroid 62 as shown in FIGS. 34A and 34B.    -   6) Plasma etch    -   7) Glass etch    -   8) Chemical clean the surfaces of layers 160 and 161    -   9) Shadow Process the surfaces of the interconnecting holes    -   10) Copper plate the surfaces and the holes    -   11) Chemical clean    -   12) Vacuum laminate dry film    -   13) Expose the fifth and sixth circuit layers 160, 161 for        etching    -   14) Etch the fifth and sixth circuitry layers 160, 161 to form        printed circuits from the plated foils 160, 161    -   15) Strip dry film from surface of the fifth and sixth layers of        printed circuitry    -   16) Chemical Clean    -   17) Vacuum bake    -   18) Laminate two covercoats or apply cover layers or solder        masks 170, 171 over the fifth and sixth printed circuit layers        (as shown in FIG. 22) while including appropriate openings to        accommodate components to be assembled there-on    -   19) Bright tin/lead plate or apply protective coating onto the        exposed copper circuitry underneath the covercoat openings    -   20) Separate each individual assembly by routing or cutting        apart the individual rectangular circuits each containing an        embedded individual ferrite toroids and six circuitry layers    -   21) Test    -   22) Assemble electrical circuit elements onto the individual        miniature inductor or transformer components as shown in FIGS.        23 and 34A, 34B    -   23) Test the final assembly

The assembly described above and shown in FIG. 23 has six layers ofprinted circuitry and two plated through holes 95 and 120 through eachhole (via) 80, 81 formed in the support panel 56 around the outside andinside of the embedded toroidal ferrite. In the assembly shown, thefirst, second, third and fourth printed circuitry layers and platedthrough holes 95 and 120 form circuitry and the windings of an inductoror transformer.

By way of specific example, FIG. 23 illustrates an embodiment of aminiature power supply 195 constructed in accordance with thisinvention. As shown, the magnetic components of the power supply areentirely encapsulated within the printed circuit board. By way ofspecific example, the support panel for this embodiment has a length of2 3/16 inches and a width of 1 13/16 inches.

In the foregoing embodiment, ferrite toroids are used to form inductorsand transformers in the plane of the circuit board or flexible circuit.It will be understood that other types of magnetic or ferriteconfigurations may be utilized, such as oval shaped toroidal ferritestructures and ferrite slabs having various geometric configurations orother magnetic materials. In other embodiments, the through holeconductors are formed by processes other than copper plating, insteadutilizing, for example, conductive pastes. In addition, the pluralplated through holes insulated from each other may be formed directlythrough the magnetic material. Construction of such another embodimentof the invention is shown in FIGS. 24-26. In this embodiment, themanufacture of a multiple through hole assembly utilizes a slab offerrite material and vias drilled are formed through the ferrite slab.Plural conductive through holes are formed in each via.

As shown in FIG. 24, a plurality of rectangular openings 200 are formedtypically by routing, in a support panel 205. Panel 205 isadvantageously an FR-4 epoxy laminate sheet although it will be apparentthat sheets made from other materials including other types of sheetsused for circuit board fabrication are applicable for use as supportpanel 205. In this embodiment, the openings are formed completelythrough the support panel.

Ferrite plates 210 are respectively embedded within the openings 200, asshown in FIG. 25. Each of these ferrite plates 210 serve as aferromagnetic slab on which is fabricated inductive components. Asdescribed below, these plates 210 may be formed as shown in FIG. 25without through holes which are subsequently drilled during constructionof the component. In other embodiments a plurality of through holes, asseen in FIG. 27, may be pre-formed during molding of ferrite slabs.

The ferrite plate 210 is shown in cross-section in FIG. 26. This figureshows the surface of the ferrite plate 210 including the walls of itsthrough hole openings 215 covered with an insulating layer 220.Advantageously, this layer is formed by a vacuum deposited parylenecoating as described in detail above. Layer 220 insulates the ferritematerial from the copper circuitry to be fabricated over the ferritesurface and on the walls of the through holes in the ferrites. Thiscoating is advisable or necessary for low resistivity ferrites, e.g.,high permeability ferrites of the order of 2300 PERM. Coating 220 willoften not be utilized for lower permeability ferrites, such as 350 PERMferrites having a higher resistivity.

Copper foils 225, 226 are then respectively laminated to the top andbottom surfaces of the ferrite plate 210 using an epoxy prepreg 230 orother suitable adhesive to affix the foil to the ferrite plate.Depending upon the ultimate application of the inductive component, thecopper foil will typically also cover all or part of the support panel205. In this lamination step and the lamination steps described below,the materials used are selected to provide the desired physicalproperties for the finished circuitry. These properties are commonlyreferred to as peel strengths and bond strengths. The preferredmaterials for laminating are: Crystal, B-1000, R1500 from Rogers Corp.,Pyralux FB from Dupont, Calif. 338, CA 333, E33 from Shin-Etsu, AY50KA,CY2535KA, CVK2,530130, SAU, SPC, SPA from Arisawa, and Medium or High Tgepoxy prepregs from Isola.

Through holes or vias 215 in the ferrite plates 210 (shown in FIGS. 26and 27) enable fabrication of plated through conductors. These platedthrough vias function as electrical windings for the inductor ortransformer device. These holes are typically 12 to 50 mil in diameterbut can be larger or smaller, (e.g., as small as 4 mil in diameter)depending upon the specifications of the inductor or transformer beingmanufactured. In some embodiments, the ferrite plates are molded orotherwise pre-formed with the desired through holes 215. In suchembodiments, through holes using conventional drilling equipment aredrilled through the copper foil after the foil is laminated to theferrite plate 210. These holes are drilled so as to register with thepreformed holes in the ferrite plates. In other embodiments, such as theferrite plates 210 shown as FIG. 215, the ferrite plates are notpre-formed with holes. In these embodiments, the holes are formed in theferrite plates 210 after lamination of the copper foils 225, 226.Drilling holes through the ferrite plates and copper foil isadvantageously performed using laser drilling equipment.

After drilling, the laminated panels are advantageously plasma etched toclean the drilled holes. This step is advantageously followed by a glassetch to remove spurious glass particles from the holes 215 followed bychemically cleaning the top and bottom surfaces of the exposed copper.

A conventional process is then used to chemically coat (shown at 245)the top and bottom surfaces of the copper foil in preparation of copperplating these top and bottom surfaces as well as the inside surface ofall of the through holes 215. This process is commonly referred to asthe SHADOW process. An article describing the process entitled “TheReliability of PTH Printed Wiring Boards Manufactured With aGraphite-Based Direct Metallization Process” is included with thisapplication as Appendix A.

Following the application of the chemical coating 245 using the SHADOWprocess, the subassembly is copper plated. The plated copper is shown inFIG. 26 and covers both the copper foil laminate 225, the copper foillaminate 226 and the internal walls of the through holes (vias) 215(shown at 230) so as to electrically connect the top and bottom copperfoils 225, 226 via the plated through holes 230.

Printed circuits are then fabricated using the top and bottom layers ofcopper laminate and plated copper. These circuits are advantageouslyformed by vacuum laminating a dry photographically developable film overthe surfaces of the plated copper on the top and bottom of thesubassembly.

Using standard techniques of printed circuitry, first and second layersof circuitry are fabricated by using the dry film to mask the desiredcircuitry. The unmasked copper is then etched from both top and bottomsurfaces of the component assembly. The remaining dry film mask is thenstripped from those top and bottom surfaces. The remaining copper formsa first layer of circuitry 250 on the top surface, as shown in FIG. 26,and a second layer of circuitry 251 on the bottom surface,interconnected by the copper plate via holes 230.

The top and bottom surfaces are then chemically cleaned. The componentassembly is then vacuum baked to remove any remaining surface chemicalsor moisture.

The component assembly is then prepared for an additional copper layerand an additional plated via insulated from but fabricated over thefirst copper layers. An insulating coating is used to separate themultiple layers of circuitry and plated vias. Epoxy, parylene, liquidpolymide and other materials may be used. However, as described above,parylene coating has been discovered to be particularly advantageous forforming these insulating layers. In this process, the parylene is vacuumdeposited over the entire subassembly to leave, as illustrated in FIG.26, a thin coating 270 over the top layer of circuitry 250, a thincoating 271 over the bottom layer of circuitry 251 and a thin coating272 inside the copper plated through hole 230.

In preparation for parylene coating, a very thin Silane and/or Carboxyllayer is deposited on the subassembly using a PECVD process (PlasmaEnhanced Chemical Vapor Deposition).

The parylene coating process is further described in the publicationentitled “Parylene Conformal Coatings Specifications and Properties,”published by Specialty Coating Systems, Indianapolis, Ind. and attachedas Appendix B to this application. This parylene coating is pinhole freeand has a high dielectric strength with very thin coatings providingvery high voltage breakdown values. By way of specific example, parylenecoatings formed of Parylene C with thicknesses of 0.0005 mil to 0.001mil provide a voltage breakdown guard band of about 5600 volts per milof thickness. Parylene C has a dielectric constant of about 2.28.

Nova HT Parylene described in Appendix C to this application provides aneven higher dielectric constant of about 3.15 and provides a voltagebreakdown of about 750 volts per micron of thickness. As a result, verythin coatings, e.g., 10 to 15 microns provides a breakdown voltagebarrier in the range of 7500 volts or higher.

One embodiment of the parylene coated subassembly is shown in FIG. 27.This and other parylene coatings shown in other photographs were coatedat the SCS Coating Center at Ontario, Calif., as described in Appendix Dto this application.

Following application of the parylene coating, this subassembly isplasma burned in preparation for additional layers of circuitry over inthe top circuit layers and bottom layer 250, 251.

Formation of third and fourth layers of circuitry begins with drillinghole openings in copper foil sheets 280, 281 that will register over thecircuitry openings shown in FIG. 26. Similar openings registering withthese through hole openings are drilled in two sheets of adhesive 285,286. A low temperature lamination process is then used to partiallylaminate the pre-drilled copper foils 80, 81 to the pre-drilledadhesives so that the respective openings are aligned as shown in FIG.26. The adhesive coated copper foil 280 is then attached to the surfaceof the parylene coated top surface of this first circuitry layer 250 andthe adhesive coated copper foil 281 is attached to the surface of theparylene coated second circuitry layer 261.

Copper foils 280, 281 are then laminated to the subassembly at hightemperature and pressure to form a four copper layer assembly with thethird layer 280 and the fourth layer 281, respectively, insulated fromthe circuitry layers 2 by the respective parylene coating layers 270,271.

The surfaces of copper foils 280, 281 are now chemically coated usingthe SHADOW process. Following the application of a chemical coatingusing the SHADOW process, the subassembly is again copper plated. Theplated copper is shown in FIG. 26 and covers both the copper foillaminate 280 (as shown at 290), copper foil laminate 281 (as shown at291) and the parylene coated walls of the plated through holes (vies)230 (shown at 300) so as to electrically connect the third and fourthcopper plated foils 280, 281 via plated through holes 300.

Third and fourth printed circuits are then fabricated using the top andbottom layers of plated copper foils 280, 281. These circuits areadvantageously formed by vacuum laminating a dry photographicallydevelopable film over the top and bottom surfaces 280, 281 of the platedcopper.

Using the well known conventional techniques of printed circuitry, thesethird and fourth layers of circuitry are fabricated by using the dryfilm to mask the desired circuitry. The exposed, i.e., unmasked copperis then etched from both top and bottom surfaces of the componentassembly. The remaining dry film mask is then stripped from those topand bottom surfaces. The remaining copper forms the desired third layerof circuitry on the top surface, the fourth layer of circuitry on thebottom surface, and the circuitry connections between the third andfourth layers connected to the copper plated via holes 300.

The top and bottom surfaces are then chemically cleaned. The componentassembly is then vacuum baked to remove any remaining surface chemicals.

Additional through hole connection holes may now be selectively drilledthrough the respective copper sheets and panel 205 to enable, forexample, through hole connections for the circuit elements located overthe ferrite plate 210.

Additional fifth and sixth layers of circuitry 305, 306 are fabricatedover the third and fourth layers. In the embodiment shown in FIG. 7,these circuit layers are insulated from the adjacent third and fourthlayers by a relatively thick single or two or more layers of prepreg310. By way of example, the Isola medium Tg epoxy prepreg has a voltagebreakdown rating of 1100 to 1200 volts per mil thickness. By way ofspecific example, a 4 mil thickness of this prepreg was used to providea voltage breakdown of over 4000 volts. These fifth and sixth layers areformed following the cleaning and baking steps as follows:

-   -   1) Drill the fifth and sixth layer copper foils with tooling        holes    -   2) Drill tooling holes in two sheets of adhesive, or prepreg    -   3) Kiss laminate predrilled two copper foils with predrilled        adhesive    -   4) Lay up adhesive coated copper foil and prepreg with panels        containing layers 1, 2, 3, and 4    -   5) Laminate all the material together at high temperature and        pressure using ordinary (vacuum) lamination process so the        result is a six copper layer assembly with layers 1 and 2        interconnected via the plated holes and layers 3 and 4        interconnected but isolated from layers 1 and 2 using the same        holes    -   6) Drill additional connection holes on the six layer assembly    -   7) Plasma etch    -   8) Glass etch    -   9) Chemical clean the surfaces of layers 5 and 6    -   10) Shadow Process the surfaces of layers 5 and 6 and the        interconnecting holes    -   11) Copper plate the surfaces and the holes    -   12) Chemical clean    -   13) Vacuum laminate dry film    -   14) Expose layers 5 and 6 circuitry for etching    -   15) Etch layers 5 and 6 circuitry    -   16) Strip dry film from surface of layers 5 and 6    -   17) Chemical Clean    -   18) Vacuum bake    -   19) Laminate two covercoats or (apply cover layers-new) over        layers 5 and 6 with appropriate openings to accommodate        components to be assembled there-on    -   20) Bright tin/lead plate or (apply protective coating-new) onto        the exposed copper circuitry underneath the covercoat openings    -   21) Separate each individual assembly by routing the individual        rectangular circuits each containing individual ferrite towards        with 6 circuit layers    -   22) Test    -   23) Assemble components onto the individual rectangular circuits    -   24) Test the final assembly

The assembly described above and shown in FIG. 26 has six layers ofcircuitry and two plated through holes 230 and 300 through each hole(via) 215 formed in the ferrite plate 210. In the assembly shown, thefirst, second, third and fourth circuit layers 225, 226, 280 and 281 andplated through holes advantageously form the windings of a “virtualtoroid” inductor or transformer constructed in accordance with pendingU.S. patent application entitled Electronic Transformer Inductor Devicesand Methods for Making Same, Ser. No. 10/659,797, Publication No.2004/0135662-A1, a copy of which is attached as Appendix E.

The plated through holes and printed circuitry may also be used toconstruct other embodiments of inductors and transformers. Examples areCell Core transformers also described in the pending application,Appendix E.

The processes described above can be used to produce multipleindependent through holes in ferrite and other materials such as printedcircuit board and flex. Thus, additional layers of copper foil andcopper plate advantageously insulated by a parylene coating allowsadditional independent plated conductors in a single via.

In other embodiments, a third or fourth plated conductive through holeeach insulated by a layer of parylene, are constructed in the mannerdescribed above to provide, for example, additional turns around theferrite core or additional through hole connectors for circuitry on thesupport panel. FIGS. 29, 30, and 31 are photomicrographic views ofcross-sections of printed circuit board in which plural plated throughhole circuits are formed in vias of the board. FIG. 29 illustrates twoconductors constructed in a single via as described above. FIG. 30illustrates three plated through hole conductors in a single via andFIG. 31 illustrates four plated through hole conductors in a single via.

Another embodiment is shown in FIGS. 31A, 31B, 32A, 32B, 33A, 33B, 34A,34B, and 35. In this embodiment, each electrical component incorporatestwo inductors of different sizes embedded into the support panel. Thecomponent shown is an extremely small power supply constructed on apanel 250 which is only 2.000 inch long by 1.500 inch wide. In thispanel are formed two toroidal cavities. Toroidal ferrites havingdifferent outside diameters are situated in these cavities. Using theprocess described above and illustrated in FIGS. 1-22, a first printedcircuit is etched in the top layer of the panel and a second printedcircuit is etched in the bottom layer of its panel. The first printedcircuit layer includes respective primary windings 255 and 260 shown inFIG. 31A. The second printed circuit layer includes primary windings 265and 270 shown in FIG. 31B. Also shown are the plated through holes 275,276, 277, and 278, drilled outside and inside the respective toroidalferrites, and plated in the manner described above. Printed circuits255, 265 and plated through holes 275, 276 form the windings of aninductor. Printed circuits 260, 270 and plated through holes 277, 278form the primary windings of a transformer.

Following a parylene coating as described above, a third printed circuitis formed in its top surface and a fourth printed circuit is formed onits bottom surface of the sub-assembly as shown in FIGS. 32A and 32B. Inaddition second plated through holes 295, 296, 297 and 298 arerespectively formed in this same through holes as plated through holes275, 276, 277 and 278 but insulated therefrom by the parylene coating.The third printed circuit layer includes additional windings 300 and305. The fourth printed circuit layer includes additional windings 310,315.

Printed circuits 300, 310 and plated through holes 295, 296 from anotherset of windings for the inductor. Printed circuits 305, 315 and platedthrough holes 297, 298 form the secondary winding of the transformer. Inthis example show, the transformer is a step-down transformer having 32primary windings and 4 secondary windings to provide an 8 to 1 turnsratio transformer.

A fifth printed circuit 325 is formed over the top surface of the topsubassembly the third printed circuit layer as shown in FIG. 33A. Asixth printed circuit 330 is formed in the bottom surface of thesubassembly as shown in FIG. 33B. The circuitry elements for completingthe power supply are attached as the respective surface of thesubassembly. An aspect of the construction shown that contributes to theminiaturization of the electronic component is that the fifth and sixthprinted circuitry 325, 330 and attached circuit elements can utilize theentire surface of the support panel including the surface space over theembedded ferrite toroids. As such, the resulting power supplies andother components utilizing inductors and transformers can be constructedconsiderably smaller than conventional surface mounted transformers andinductors.

The above presents a description of the best mode contemplated for thecomponents and methods of manufacturing said in such full, clear,concise and exact terms as to enable any person skilled in the art towhich it pertains to produce these components and practice thesemethods. These components and methods are, however, susceptible tomodifications that are fully equivalent to the embodiment discussedabove. Consequently, these components and methods are not limited to theparticular embodiment disclosed. On the contrary, these apparatuses andmethods cover all modifications coming within the spirit and scope ofthe present invention.

1. A method for making plural plated through holes in a single circuitboard via comprising plating copper in the walls of said circuit boardvia to form a first plated through hole, applying a thin layer of firstadhesive promotor to the surface of said plated via, vacuum deposit anorganic layer having a high dielectric strength unto said layer of firstadhesive promoter, applying a second layer of adhesive promoter oversaid layer of polymer, and plating copper over said second layer ofadhesive promoter to form a second plated through hole in said circuitboard via.
 2. The method of claim 1 wherein said first adhesive promoteris applied by a PECVD process (Plasma Enhanced Chemical VaporDeposition).
 3. The method of claim 1 wherein said first adhesivepromoter is Silane, Carboxyl or Silane and Carboxyl.
 4. The method ofclaim 1 wherein said first adhesive promoter is applied by dipping thethrough holes in the adhesive promoter.
 5. The method of claim 1 whereinsaid second adhesive promoter is applied by a PECVD process.
 6. Themethod of claim 5 wherein said second adhesive promoter is a Carboxl orSilane gas phase chemical reaction.
 7. The method of claim 1 whereinsaid organic layer is a vacuum deposited.
 8. The method of claim 7wherein said organic layer is a parylene coating.
 9. A method for makingplural insulated conductor through holes in a single circuit board viacomprising: applying a first conductive layer on the walls of saidcircuit board via to form a first conductor through hole, applying alayer of first adhesive promoter to the surface said first conductorlayer, depositing a thin organic layer having a high dielectric strengthonto said layer of first adhesive promoter. applying a second layer ofadhesive promoter on said organic layer, and applying a second conductorlayer over said second layer of adhesive promoter.